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Sunday, October 21, 2012

MAGIC of knowledge

I turned the switch on and BOOM! That noise, the tiny puff of smoke and the accompanying smell had become far too familiar.

I looked on in confusion at all the failed electronics components in front of me. I needed answers. Why did the H-bridge circuit not work as “claimed”? Books showed numerous such circuits. The Internet was not short of designs either. They were all similar though. I had done my research. I thought I understood the principles and modalities of operation. Then, where did the fault lie? Frustration was creeping in. But I just had to find the fault and fix it.

I wanted to make the SMPS based inverter because I could learn so much in a field completely new to me and then use the inverter at home during power cuts. In that one night of experimentation, I had failed repeatedly, damaging 24 IR2110’s and a lot more components. I had applied all I had learned thus far. Success, however, eluded me.

After repeated failures, I posted my problem on online electronics forums. Numerous members from around the world, engineers and non-engineers alike, joined in to contribute. I learnt and questioned. Heated discussions, arguments and counter-arguments took place. And I absorbed all I could. I did not get a direct solution to my problem but I felt I had become richer and perhaps, through discussion, helped make others richer.

I spent hours reading documents and application notes, analyzing existing designs and testing the different concepts experimentally. However, the result was the same.

One day I stumbled upon a circuit on the internet, which had a different type of MOSFET gate protection, which employed a resistor between “gate” and “source”. Theoretically this resistor was not required. I redesigned the entire circuit with these resistors connected.

MAGIC! I got the required AC output. No BOOM, no smoke, no smell! 4 resistors (one between gate and source of each MOSFET) that, in total, cost less than $0.25, had been the difference! This was the magic of knowledge – the power of knowledge people refer to.

I then resorted to books and the Internet and learnt why the gate-to-source resistor stopped the MOSFET, and in turn the driver IR2110, from “blowing”.

After completing my inverter, I regularly posted on online electronics forums, especially www.edaboard.com – in the time I found between school, sports, electronics endeavors and other activities – to help others and to learn.

Many people later posted on www.edaboard.com regarding problems where the MOSFET and driver “blew”. I had been the one to suggest the use of the “gate-to-source” resistor and this had been the solution to most such problems.

My repeated failures had frustrated me, but also pushed me beyond the boundary of books to learn, acquire and share knowledge, to believe in the power of knowledge but most importantly to believe in myself and my capabilities. This belief and these teachings helped me in later endeavors to overcome obstacles in my way and achieve success.

--------------------------------------------------------------------------------------------------------------------- Importance of the gate-to-source resistor:

It prevents accidental turn on of the MOSFET by external noise usually
at startup when the gate is floating. The MOSFET may sometimes turn on
with a floating gate because of the internal drain to gate "Miller"
capacitance. A gate to source resistor acts as a pull-down to ensure a
low level for the MOSFET. I have had MOSFETs blowing up in high voltage
circuits, without the resistor in place. In most of the commercial power
supplies / inverters I have seen, there is a 1k resistor used.

A similar experience is narrated in Sanajaya Maniktala's "Switching
Power Supplies A to Z". This is also talked of in Raymond Mack's
"Switching Power Supplies Demystified".

Use a gate-to-source resistor for each individual MOSFET but make each resistor larger so that the parallel combination gives about 1k or so. For example, if you have 3 MOSFETs in parallel, use 3.3k resistors for each MOSFET.

your blog is awsome. really giving lots of clues to get out of the problem of driving MOSFETS using IR2110.

I need your help here.

Can you please send me "IR2110 circuit for high-voltage full-bridge drive control using 2 input signals" for ISIS PROTEUS

Secondly I wish to drive a 220VDC Motor 10A (that makes it around 3HP DC MOTOR and theoretically speaking the starting current must be 3 to 4 times the normal current which will be around 40A @ 220VDC) can you help me in the circuit design if you have any can you please send it to chughtai_farhan@yahoo.com

Thirdly, I wish if you could send me your cell phone number incase I need to talk to you.

Yes it would. And it would be even better since you can use any duty cycle between 0% and 100% (inclusive).

Just remember to have a means of controlling the drive via an isolated drive system, since the two "grounds" will now be different. A simple solution is to use an optically isolated driver such as TLP250 or the better(and more expensive) HCPL3120.

Only for low frequency such as 50Hz or 60Hz. And even then it is advisable to use a totem-pole stage after the optocoupler. 4N25 and other "general purpose optocouplers" can NOT - should not - be used for high frequencies in the tens of kiloHertz.

For SPWM, the frequency doesn't directly affect performance, since the wave will be filtered to produce a 50Hz / 60Hz output. However, the frequency will affect the operation of the MOSFETs/IGBTs and optimum frequency should thus be chosen. 16kHz is a good frequency to choose. The higher the frequency, larger the switching losses but smaller the required inductance and capacitance. And vice versa.

Salambrother the circuit files can't be accessed through the link that u gave in above comments of urz.... i.e.http://rapidshare.com/files/4214258713/IR2110%20circuit%20for%20high-voltage%20full-bridge%20drive%20with%20tied%20switch%20control%20-%20control%20with%202%20input%20signals.zip

plz upload the files somewhere else or re-new it... it says the download has been restricted by the uploader.... regards

Thanks for your reply. Regarding diodes I must have made a mistake while drawing the schematic I will reassure it

Regarding putting 7812 i was thinking on the same lines. To give you more closer look into the VCC, VD and VB voltages applied

VCC = VD = 15V VB = 18V without regulator

I am very curious about this question

1. Why Side A is working fine and Side B IR always fails to work on High Side 2. And as mentioned in my PDF, When there is no load connected both the sides work fine (the polarity changes with the change in input signals) and gives the output of 300VDC @ 100% duty cycle. The problem only occurs on one side when the load is connected (TO MENTION WITHOUT LOAD IT WORKS FINE).

Can you please put a light on above mentioned points.

In the meanwhile I will be working on the points you mention and will post the results soon.

The resistor functions to prevent accidental turn on of the MOSFET. A zener diode won't do that. The zener diode will only protect against over-voltages. For over-voltage protection, a zener diode may be added. However, for prevention of accidental turn on of the MOSFET, a gate-to-source resistor must be used.

Hello Tahmid, first of all thanks for this blog. I learnt lot from this side. Can you guide me to build transistor based high and low side mosfet driver. Here bridge dc volt is 320volt.Thamks & regardskunal

About gate-protecting resistors, I use to put that kind of protection in HIN and LIN (pull down to logic ground), ensuring a default state of "inactive" until (in my case) a PIC is ready to drive them. Is this kind of protection equivalent to the one depicted in your schematics?

I don't think that's enough. It isn't the same as the ones depicted in my schematics. If you see the IR2110 block diagram, you will find that the HIN and LIN pins have internal pull-down resistors. Despite this, the MOSFETs are not protected. So, I don't think that placing external pull-down resistors on HIN and LIN pins will help much.

I'm using the IR2110 as a High/Low side driver for switching two IRF740s and an inductive load. The high side is driven by a bootstrap capacitor and diode as described in the application note. Using a gate/source resistor does not work in this configuration as it seems to drain the bootstrap capacitor, preventing the high side to switch. The low side resistor works fine to pull down the gate.

I need a solution for a defined state of the high side gate, that's capable of handling the level switching of VS because the high side is now always on as soon as the low side is switched on. Even when Hin is tied to ground, the high side switches in phase with the low side. I guess this has to do with my choice of bootstrap capacitor/diode combination, but it doesn't seem very robust to me.

Any ideas how to solve this? Care to elaborate on the bootstrap capacitor/diode types?

The gate-source resistor will slightly drain the capacitor but you should be able to compensate with a slightly larger capacitor. Plus, the resistor will not prevent the high side from switching. If you have a large enough capacitance, there will be no problem with the resistor in place. All my circuits use the resistor with no problem.

Tahmid, actually I was only looking how to wind my transformer, but started reading all this cool stuff. The I remembered there exist circuits using resonance, becoming more popular all the time. Is there a reason you don't mention them (have I missed it, are they difficult, not your "thing", do they have a too low range)?

Thank you for the great information. can you pls check this circuit (http://3.bp.blogspot.com/_aYp-sOZZbj0/TOpbFp-3gEI/AAAAAAAAAuA/fCi1KNMiJmw/s1600/pic16f877a+stabilizer1.png) there is a 100k resister grounded instead of 1k. can I use 1k? if not what resister you suggest for driving and grounding?

Unless you're using this at a very low frequency, this is a bad circuit. You should use a good MOSFET driver circuit. Replace R8 and R10 with resistance between 10 ohms to 33 ohms. Replace R9 and R11 with resistances 1k to 2.2k.

Usually it's the high-side responsible for blowing up the H-bridge (from my experience). However, the low-side can also be a problem. I've had issues with low-side MOSFETs in push-pull converters when I didn't place the gate-to-source resistor.

Hi Tahmid, i´m using a TL494 to generate the PWM signal and an isolated power supply for the high channel of the IR2110 because i need a duty cicle varible from 0 to 0,45.I read that you would recomend a optically isolated driver in this case (TLP250 or HCPL3120)How would you conect this ic´s in a half bridge configuration?

You'd need one optically isolated driver per high-side MOSFET. Both high side drives must have individual isolated supplies. You can use one supply for both low side MOSFETs. That means you'd need three isolated supplies.

You can use IR2110 for this as well. That would avoid you having to use so many different supplies.

i am working out at inverters and i am using PWM signals to drive the mosfet in h-bridge system. i want the circuit as simple as possible for my colleagues. I have generated PWM signals now i wish to use IR2110 to drive the mosfet. but i don't understand why would i be supplying two different supplies for IR2110 and how would i be managing such a supply. i would be very helpful to you if you help me on this. thanks

What do you mean by two different supplies? You should be able to use one supply and derive the required voltages from there. Eg. 12V for the VCC and 5V for VDD can be derived with a 7805 from the 12V.

The mosfet driver cct are ok. The power mosfet cct for a half bridge dc-dc converter are ok too. however when both cct are link up, the output voltage is "add on" onto the hi side of the mosfet gate input.

I couldn't understand your question. What do you mean by "add on"? Are you measuring gate voltage with respect to ground? If that comes to be Vsupply (supply voltage for half-bridge circuit) + Vdrive (drive voltage from driver circuit), then that is correct. Remember that for the high side drive, the driver's output 10V (or whatever it is) is from gate to source. Source itself will be at ~Vsupply when on.

MR TAHMID, thanks for your effort for most people looking for help,but almost all your code is in mikro c and this software is very expensive ,if I have that sum of money I will not bother to build sine wave inverter ,I go straight to buy China made quality sine wave inverter majority of people In this blog are hobbyists and not commercial manufactural,please try to also provide the hex file for the one you want to give out and the one you want keep let people know. Parker from ancient city of Benin

Hey! There is a free version of mikroC which I have used. My mikroC code on this blog can be run on the free version of mikroC. However, after using XC32, I have been developing a bit in XC8 and may continue 8-bit PIC projects in XC8 in the future. That has a free version too, except with no code size limitation like mikroC.

Hi Tahmid,I'm designing a dc motor H-bridge driver. Motor rating would be 220V dc.I would like to discuss the effect of back emf of motor.Say the back emf is 200V, Q1,Q4 on. How long will the charge of bootstrap capacitor C1 last.Shall I need to stop the motor for switching Q2 on to charge the capacitor at frequent intervals?What should be the voltage rating of C1/C2?

Hi Tahmid, do you have tested LM5111-1 features? I have try to use them but, despite i have followed all TI instructions and applications note, the LM5111 burn out itself with or without load. I have resistance on gate to source, diode on gate paralleled to gate resistor and the circuit work with 5V at side of driver input, 12V at the MOS side. Thank's.

Dear Tahmid,I've read about everything you posted about H Bridges and controllers. Very informative and I guess a lot of us did learn quite a bit following your tracks.I'm a (rather) old electronician now but I keep learning... (aren't we all ?).I have 3 questions :1) I want to control a load with a setup very similar to your fig. 7 on your page http://tahmidmc.blogspot.be/2013/01/using-high-low-side-driver-ir2110-with.htmlThe frequency is 1 KHz but the upper CMOS are turned on but a fraction of the 1000 periods every second (for example ON for the 123 first cycles, then OFF for the 877 next cycles). The "on" period numbers vary almost randomly every seconds.As I see it, if I were to build an H-Bridge with a bootstrap, as long as the 2 lower CMOS switches are active once every cycle the bootstrap cap will remain sufficiently charged. Am I right ?(hehe, I feel like a nubie, but electronic is a bit like medicine: although they're both doctors, you won't ask a dentist to practice brain surgery, and I'm far from my expertise domains here)

2) I intend to use the HIP4081: One can find a very nice and useful application note here : http://www.hvlabs.com/files/HIP4081application.pdfTo make a long story short, all calculus made, my bootstrap cap should be 93 nF (say 100 n). BUT if you add your "magic" 1K resistor, the charges drained out of the boostrap cap are wayyyy larger. And I did not even take the diode in parallel on the serie gate resistor into account (well, ok, 20 nano Coulomb is prolly negligible)... I suppose that the magic 1K is the reason why you use large bootstrap capacitors, but HOW do you calculate their value ? We all have used "educated guess" but this looks a bit too shamanic for me.

3) a bit off subject, but knowing that my load is essentially capacitive, do you see any particular things I should pay attention to ?

I'm eager to read your comments. Thanks again for the wealth of information you gave to us.Jacques from Brussels

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About Me

I am Syed Tahmid Mahbub, from Dhaka, Bangladesh, born on August 1, 1994.
Electronics is my passion and from class V, I have been learning electronics. I learnt and worked mostly on SMPS, power electronics, microcontrollers and integration of microcontrollers with SMPS and power electronics. I've used PIC and AVR microcontrollers - PIC 10F, 12F, 16F, 18F, 24F, dsPIC 30F, 33F, PIC32, ATmega and ATtiny, integrating them with various SMPS and power electronics circuits.
I have completed my Bachelor's degree from Cornell University (Class of 2017) in Ithaca, New York, USA, majoring in Electrical and Computer Engineering (ECE).
I am a member of the forum www.edaboard.com, where I am an "Advanced Member Level 5" (the highest level attainable) and also the forum allaboutcircuits.com, where I am a "Senior Member". I post to help solve electronics-related problems of engineers and engineering students from all over the world.
I love watching and playing cricket and football (soccer), and listening to music.
I am now a hardware engineer at Apple in Silicon Valley, California, USA.